Potential responses of vegetation to atmospheric aerosols in arid and semi-arid regions of Asia

Changes in atmospheric aerosols have profound effects on ecosystem productivity,vegetation growth and activity by directly and indirectly influencing climate and environment conditions.However,few studies have focused on the effects of atmospheric aerosols on vegetation growth and activity in the vulnerable arid and semi-arid regions,which are also the source areas of aerosols.Using the datasets of aerosol optical depth(AOD),normalized difference vegetation index(NDVI)and multiple climatic variables including photosynthetically active radiation(PAR),surface solar radiation(SSR),surface air temperature(TEM)and total precipitation(PRE),we analyzed the potential responses of vegetation activity to atmospheric aerosols and their associated climatic factors in arid and semi-arid regions of Asia from 2005 to 2015.Our results suggested that areas with decreasing growing-season NDVI were mainly observed in regions with relatively sparse vegetation coverage,while AOD tended to increase as NDVI decreased in these regions.Upon further analysis,we found that aerosols might exert a negative influence on vegetation activity by reducing SSR,PAR and TEM,as well as suppressing PRE in most arid and semi-arid regions of Asia.Moreover,the responses of atmospheric aerosols on vegetation activity varied among different growing stages.At the early growing stage,higher concentration of aerosol was accompanied with suppressed vegetation growth by enhancing cooling effects and reducing SSR and PAR.At the middle growing stage,aerosols tended to alter microphysical properties of clouds with suppressed PRE,thereby restricting vegetation growth.At the late growing stage,aerosols exerted significantly positive influences on vegetation activity by increasing SSR,PAR and TEM in regions with high anthropogenic aerosols.Overall,at different growing stages,aerosols could influence vegetation activity by changing different climatic factors including SSR,PAR,TEM and PRE in arid and semi-arid regions of Asia.This study not only clarifies the impacts of aerosols on vegetation activity in source areas,but also explains the roles of aerosols in climate.